Prior art carboxylic acid syntheses from aromatic ketones by the addition of hydrogen cyanide such as that disclosed by Eliel et al., in Organic Syntheses, 33, 7 (1953) involve a reversible step with an unfavorable equilibrium as well as a reduction step.
More recently, applications have been filed disclosing and claiming a process for preparing carboxylic acids by reacting glycidonitriles with a Lewis acid having a non-nucleophilic anion, i.e., an ionic Lewis acid, to form the 2-oxo-propionitrile, which is then hydrolyzed to the carboxylate salt with a strong base, and the salt is converted to the carboxylic acid with a strong acid. That process has the advantage of involving only three steps, but that process generates hydrogen cyanide gas when intermediates therein dimerize, which gas must be removed.
Also, applications have been filed disclosing and claiming a process for preparing carboxylic acids from glycidonitriles through enol acylates via a hydrohalogenation-acylation-dehydrohalogenation procedure, involving the use of hydrogen halide to effect halogenation and opening of the oxirane ring of the glycidonitrile starting material to form the 3-halo-2-hydroxy-propionitrile, acylation and dehydrohalogenation of the 3-halo-2-hydroxypropionitrile to form the enol-acylate (2-acyloxy acrylonitrile), followed by hydrolysis of the enol acylate with base to form the carboxylate salt, which salt is converted to the carboxylic acid with acid. This process uses more steps than the ionic Lewis acid process referred to above but permits the production of carboxylic acid from glycidonitriles in a process wherein the cyanide ion derived from the glycidonitrile is converted to an alkali metal cyanide which remains dissolved or suspended in the reaction mixture vessel to which can be added cyanide ion destroying substances.
However, in that process the hydrohalogenation, the acylation and the dehydrohalogenation are done in a sequence of steps which requires the use of relatively dilute solutions of the reactants and the use of large quantities of pyridine in the acylation-dehydrohalogenation step.
However, those in the art of process development continue to search for more efficient processes for making carboxylic acids.